Spouse visa extension as self employed

Dear guru/ All experience members
First of all I give you background of my case.
As I am a self employed and applied for my wife visa extension. I earned more that £18600. I show that amount in my tax return. I also received SEISS grant from HMRC which is a taxable income. My accountant showed that amount in state benefits and pensions im tax over view. Long story short,
When I applied for my wife visa extension on super priority service, home office ask me what sort of benefits I received. My account gave me a letter stating that I don't received any benefits but due to not having any guide line from hmrc he put SEISS grant in the state benefits and pensions clause.
After send this letter and explaining everything I received an email today stating" Although we would normally decide your application within 8 weeks from the date it was submitted unfortunately this may not be possible in your case".
Please help me is it normal procedure for replying or it is going to take long time.
As I mentioned earlier as I am not taking any benefits nor my wife. I earned more that £18600 and show in tax. SA302, tax over view and bank statements are also submitted.
How long will it take if they are not giving any decision now.
Hope you understand my case background and give me appropriate answer.
Kind regards